In recent years, research has been carried out on cell analysis, chemical reaction, biochemical reaction, biochemical separation, biochemical analysis, etc. using a microchip called a micro total analysis system (μ-TAS), a microchip called a lab-on-a-chip, or a microchip called a micro electro mechanical system (MEMS). Such a microchip includes a plate having sides of several centimeters. The plate has formed therein a flow path of micrometer order and several types of sample introduction holes. The flow path is branched into multiple flow paths, while the branched flow paths join.
The microchip is a system adapted to react, separate and analyze a solution by causing the solution to flow in the flow path (refer to Japanese Patent No. 3402635 B2). It is known that the system is capable of reacting, separating and analyzing a small amount of a sample and improving the efficiency of the reaction. The microchip has attracted attention.
On the other hand, research has been carried out on a technique for generating a fine emulsion (droplet) in a micro flow path in the fields of chemicals, cosmetics, electronic members or electronic materials (LCD spacer and the like) or drug delivery. The emulsion is formed by using two types of fluids (such as water and oil) that are not mixed with each other due to low affinity with each other and dispersing one of the two types of fluids into the other. Typical emulsions are the following two types: a water-in-oil type emulsion formed by dispersing a water droplet into an oil phase; and an oil-in-water type emulsion formed by dispersing an oil droplet into a water phase.
The emulsion is formed using a flow path having a T-junction, for example. Referring to FIG. 14, a T-shaped flow path 101 provided with a T-junction includes flow paths 102 and 103. The flow path 102 is provided for a continuous phase. The flow path 103 is provided for a dispersed phase and perpendicular to the flow path 102. In the T-shaped flow path 101 shown in FIG. 14, water 104 is supplied to the flow path 102, and oil 105 is supplied from the flow path 103 to the flow path 102. In the flow path 101, therefore, a water-in-oil emulsion 106 composed of the oil 105 and the water 104 (that surrounds the oil 105) can be formed.
When the T-shaped flow path 101 shown in FIG. 14 is used, however, the size of the emulsion 106 varies based on the width w0 of the flow path 102. For example, when the width w0 of the flow path 102 is 100 μm, the size of the emulsion 106 is approximately 50 μm. A reduction in the width w0 of the flow path 102 is limited. It is, therefore, difficult to form a fine emulsion 106 of 1 μm or less using the microchip having the T-shaped flow path 101.
In a conventional technique, a substrate in which a flow path is provided to form an emulsion is generally made of a synthetic resin material such as polydimethylsiloxane (PDMS) (refer to JP 2008-116254 A1). However, when a fluid flows in a flow path provided in a PDMS substrate at high pressure in order to form an emulsion, the fluid pressure may cause transformation of the flow path and an increase in the width of the flow path. It is, therefore, difficult to form such a fine emulsion as described above using a microchip having the PDMS substrate.
In addition, there is a technique for forming a fine emulsion using an ultrasonic wave. However, there is a problem that the size of an emulsion particle is not constant.
It is, therefore, an object of the present invention to provide a microchip capable of forming a fine emulsion in a stable manner, and a method for manufacturing the microchip for forming an emulsion.